Self-calibrating liquid level transmitter

ABSTRACT

The present disclosure generally relates to a capacitance sensing apparatus equipped with self-calibrating capacity and method of use thereof. The disclosure contemplates the determination using a secondary means of precise fluid levels according to live possible embodiments, and the use of the determined fluid level to recalibrate the capacitance sensing apparatus along its continuous analog level, namely, a variation of the thickness of the insulation of a capacitance sensing apparatus, the variation of the surface geometry of the capacitance sensing apparatus, the use of a dual-probe sensor including a probe with a varied surface geometry, the use of an electromagnetic sensor adjoining the capacitance sensor, and the variation of the electromechanical sensor to serve as a capacitance sensing apparatus. Tile disclosure also contemplates methods for using the sensing apparatus previously disclosed to measure a fluid level using a self-calibrating capacitance sensing apparatus. Finally, the present disclosure contemplates the use of an improved mathematical method associated with a variability measurement, such as an exponential smoothing method, to determining locally discrete changes in the variability measurement of the capacitance in order to determine a fixed fluid level.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/595,135, filed on Jun. 8, 2005.

FIELD OF THE DISCLOSURE

This disclosure relates to a self-calibrating capacitance fluid levelsensing apparatus and method of use thereof, and more particularly, toan analog capacitance fluid level sensing apparatus further calibratedat fixed fluid levels with a signal from either a variable thickness inthe insulated capacitance probe, a variable geometry of the capacitanceprobe, an input from an adjoining electromechanical sensor, or an inputfrom a joined electromechanical sensor.

BACKGROUND

Varied technologies exist to measure fluid levels in containers. Thesetechnologies include but are not limited to mechanical sensors,electromechanical sensors, radar sensors, visual sensors, weightsensors, laser sensors, ultrasonic sensors, and capacitance sensors.Fluid characteristics such temperature, viscosity, conductivity,chemical abrasiveness, acidity, and the like may vary during themeasurement of sensors from one level to a second level. Thesevariations many offset measures from a sensor relying on a fixedcharacteristic to determine a precise level in a container. For example,if a mechanical sensor determines the level of a fluid by firstmeasuring the weight in a known container geometry and associated thefirst weight on a fluid level based on calculations of the volumetricdensity of the fluid, once the fluid temperature increases, thevolumetric density may decrease, raising the level above the calculatedvalue. For this reason, analogous measures performed over a long periodof time require recalibration to actual measured levels.

Fluids such as water are known to serve as proper electrical conductors.If a body of water placed between insulated plates is energized at acertain voltage (V) under the strain from the resulting dielectric forcefield, a conductive fluid is charged (Q). The capacitance (C) of a fluidis a measure of the amount of electricity stored in a fluid volumedivided by the potential of the body. The general formula for thedetermination of capacitance is C=Q/V. Tile determination of acapacitance (C) when applied to known geometries can be shown to respondto the following equation: C=kA/d, where k is the dielectric constant ofthe fluid between plates, A is the cross-sectional area of the plates,and d is the distance between the plates. It is understood by one ofordinary skill in the art that correction factors must be applied to thecalculation of any capacitance with plates and surfaces of irregulargeometries.

Capacitance sensors consist of either placing two polarized bodies at afixed voltage (V), often insulated in a conductive fluid, or placing asingle insulated body within another body and using the generalconductive container of the fluid as a pole of the dielectric forcefield. As the water level rises in the container, not only does theavailable capacitive volume increase, the contact surface of the fluidwith the polarized bodies increase accordingly.

Capacitance sensors are used in a wide range of environments, includingat extreme temperature or in toxic environment, since they require nomoving parts and are resistant to vibration, even absent a gravitationalfield. For example, cryogenic fuel levels on spacecraft are measured bycapacitance sensors. Capacitance sensors are inherently vulnerable tochanges in fluid characteristics since the dielectric constant of fluidsmay vary greatly with temperature, chemical composition, pollutants,segregation, phase changes, and other fluid characteristics. Forexample, the presence of salt or the formation of blocks of ice in abody of water can dramatically affect its measure of capacitance andultimately the fluid level determined by a capacitance sensor. Detectionbased on capacitance is also limited by nonintrusive size sensors withlimited surface area and the need to measure at low voltage levels.Capacitance sensors often operate at minimal detection levels andrequire redundant measures in order to determine a level within alimited margin of error.

Therefore, there is a need in the art for a capacitance sensor able toself-calibrate along its analog range of measurement at certain fixedfluid levels in order to limit the uncertainties associated withinherent limitations of this type of sensor.

SUMMARY

The present disclosure generally relates to a capacitance sensingapparatus and method of use thereof equipped with self-calibratingcapacity. The disclosure contemplates the determination using asecondary means of precise fluid levels according to a plurality ofpossible embodiments and the use of the determined fluid level torecalibrate the capacitance sensing apparatus along its continuousanalog measure.

In one embodiment of the present disclosure, the thickness of theinsulation of a capacitance body is varied along a precise functionalong its vertical axis. The variations at determined levels creates achange in the variability measurement of the capacitance of the fluidleading to a recalibrating level for the capacitance sensor. In anotherembodiment of the present disclosure, the surface geometry of thecapacitance body is varied along a precise function along its verticalaxis. The variations at determined levels also create a change in thevariability measurement of the capacitance of the fluid and can be usedto recalibrating the level for a capacitance sensor measure. In anotherembodiment of the present disclosure, a dual-sensor body is used where athird body has a varied surface geometry along a precise function alongits vertical axis while a first body has a regular surface geometry.Variations in the capacitance variability measurement between bothbodies are used to recalibrate the measure from the first body. Inanother embodiment of the present disclosure, an electromagnetic sensoris used together with the capacitance sensor to measure predeterminedfluid levels. In another embodiment of the present disclosure, the mainguide of an electromechanical sensor is modified to allow a guide toserve as a capacitance sensing apparatus recalibrated by theelectromechanical sensor.

The disclosure also contemplates methods for using the sensing apparatuspreviously disclosed to measure a fluid level using a self-calibratingcapacitance sensing apparatus. Finally, the present disclosure alsocontemplates the use of an improved mathematical method associated witha variability measurement, such as an exponential smoothing method todetermine locally discrete changes in the variability measurement of thecapacitance in order to determine a fixed fluid level.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments are shown in the drawings. However, it is understoodthat the present disclosure is not limited to the arrangements andinstrumentality shown in the attached drawings.

FIG. 1 is a functional side view of the self-calibrating capacitancefluid level sensing apparatus according to one embodiment of the presentdisclosure.

FIG. 2 is a partial functional view of the sensor element of theself-calibrating capacitance fluid level sensing apparatus of FIG. 1.

FIG. 3 is a top sectional view of FIG. 2 along line 3-3.

FIG. 4 is a top sectional view of FIG. 2 along line 4-4 according.

FIG. 5 is a partial functional view of the sensor element of theself-calibrating capacitance fluid level sensing apparatus of FIG. 1.

FIG. 6 is a top sectional view of FIG. 5 along line 6-6.

FIG. 7 is a top sectional view of FIG. 5 along line 7-7.

FIG. 8 is a functional side view of a dual-probe self-calibratingcapacitance fluid level sensing apparatus according to one embodiment ofthe present disclosure.

FIG. 9 is a partial functional view of the sensor element of thedual-probe self-calibrating capacitance fluid level sensing apparatus ofFIG. 8 without insulation.

FIG. 10 is a top sectional view of FIG. 9 along line 10-10.

FIG. 11 is a top sectional view of FIG. 9 along line 11-11.

FIG. 12 is a top sectional view of FIG. 9 along line 12-12.

FIG. 13 is a partial functional view of the sensor element of thedual-probe self-calibrating capacitance fluid level sensing apparatus ofFIG. 8 with insulation.

FIG. 14 is a top sectional view of FIG. 13 along the 14-14.

FIG. 15 is a top sectional view of FIG. 13 along the 15-15.

FIG. 16 is a functional side view of the sell-calibrating capacitancefluid level sensing apparatus and electromechanical sensing apparatusaccording to one embodiment of the present disclosure.

FIG. 17 is a partial side view of the electromechanical sensingapparatus of FIG. 15.

FIG. 18 is a partial side view of the electromechanical sensingapparatus with a capacitance sensing apparatus according to oneembodiment of the present disclosure.

FIG. 19 is a block diagram of the method for measuring a fluid level ina container with a self-calibrating sensing apparatus in accordance withone embodiment of the present disclosure.

FIG. 20 is a block diagram of the method for measuring a fluid level ina container with a self-calibrating sensing apparatus in accordance withone embodiment of the present disclosure.

FIG. 21 is a block diagram of the method for measuring a fluid level ina container with a dual probe self-calibrating sensing apparatus inaccordance one third embodiment of the present disclosure.

FIG. 22 is a block diagram of the method for measuring a fluid level ina container with a capacitance and electromechanical self-calibratingsensing apparatus in accordance with one embodiment of the presentdisclosure.

FIG. 23 is a block diagram of the determination method for recognitionand quantification of irregularities of a self-calibrating capacitancesensing apparatus in accordance with one embodiment of the presentdisclosure.

DETAILED DESCRIPTION

For the purposes of promoting and understanding the principles disclosedherein, reference is now made to the preferred embodiments illustratedin the drawings and specific language is used to describe the same. Itis nevertheless understood that no limitation of the scope is therebyintended. Such alterations and further modifications in the illustrateddevices and such further applications of the principles disclosed asillustrated herein are contemplated as would normally occur to oneskilled in the art to which this disclosure relates.

FIG. 1 is a functional side view of the self-calibrating capacitancefluid level sensing apparatus according to a first and second embodimentof the present disclosure. The first contemplated embodiment of thesensing apparatus to be placed in a container includes a sensor 100 witha first body 1 made of electrically conductive material, a layer ofinsulating material 7 as shown in FIG. 2 of a thickness e1 or e2 shownin FIGS. 34. The insulating material 7 is placed over the first body Icovering a first surface contact area 15 shown in FIG. 2. The sensor 100also comprises a second body 2 with a second surface contact area 101made of electrically conductive material placed in opposition to thefirst body 15.

In one embodiment, the second body 2 is a container and the secondsurface contact area 101 is the inside portion of a stainless steelcontainer, reservoir, or vat without surface insulation. It isunderstood by one of ordinary skill in the art that in order to create adifference in potential and voltage between the first body 1 and thesecond body 2, it is possible to ground the second body and place thefirst body 1 at the desired voltage in order to prevent the need for useof electrical insulation on the inner surface 101 of the second body 2.The conductive material of the first body 1 and the second body 2 in apreferred embodiment is made of stainless steel, but it is understood byone of ordinary skill in the art that any conductive material or metalmay be used.

The sensor 100 is located inside a container progressively filled with afluid 4 in order to change the fluid level from a first position 4 to asecond higher position 5. It is understood by one of ordinary skill inthe art that any fluid including a dry powder based or particular basedmedium with a minimal level of conductivity can be used as a fluid inthe scope of this disclosure. FIG. 2 illustrates an incremental changein fluid level from a first position 4 to a new position 14 quantifiedshown as ΔH where it is understood by one of ordinary skill in the artthat the symbol Δ corresponds to a mathematical differential variationdelta of height H in the fluid level. Associated with this incrementalchange is an incremental change in the contact surface of the fluid 3with the contact surfaces 7, 101 of first body 1 and the second body 2,respectively. The fluid 3 conductively connects a first fraction of thefirst surface contact area 7 on the layer of insulating material 6 to asecond fraction of the second surface contact area 101. It is understoodby one of ordinary skill in the art that in the disclosed embodiment,the second body 2 acts as the container and is progressively filled withthe fluid 4. It is also understood that the first and second fractionsof the first and second surface contact areas 7 as applied by projectionto the insulating material 6 and the second surface contact area 101correspond to the surface in contact with the fluid 3 located below thelevel 4. In the case of an increase in the level of fluid 3 by ΔH, eachof the first and second fractions of the first surface contact area 7 asapplied by projection to the insulating material 6 and the secondsurface contact area 101 is increased by an incremental surface ofheight H multiplied by a wet diameter of each surface contact area 6 and101.

Returning to FIG. 1, the sensor 100 further includes a means 21 forenergizing the first body 1 and the second body 2 at a voltage V. In oneembodiment, the first body 1 is connected via a conductor cable 13 to apower source 21 able to apply and modulate a voltage V between twoconductors bodies 1, 2. The second body 2 is also connected to the powersource 21 by a second conductor cable 11. It is understood by one ofordinary skill in the art that the induction of voltage between twoconductive bodies in association with different connectors can be madeby a very wide range of means associated with the generation andtransportation of current and ultimately voltage between bodies as knownin the art. By way of nonlimiting example, portable power sources suchas batteries, magnetically induced currents, piezoelectric currents,current generators, network-transported stabilized currents, staticfriction generators, wave-based electron excitation, wave basedtransportation of current like microwave, chemically induced currents,or even induction currents may be used as proper means to energizebodies. It is understood that while these features are described, theyare applicable to associated features on other embodiments.

The sensor 100 further comprises a means 20 for detecting thevariability in voltage as the level of fluid 4 or 5 in the containerchanges by ΔH. The means for detecting a variability of voltage may bean electronics-based circuitry used to precisely measure a voltage, suchas a potentiometer. The voltage source 21 and the associated voltagevariability measurement means 20 may also include related systems suchas current monitoring systems and magnetic field monitoring systems. Thesensor 100 may also include a system 22 for the calculation anddetermination of fixed fluid levels in the container. This system 22 isapplicable to all contemplated embodiments found in the presentdisclosure.

The sensor 100 is also equipped with a variable thickness e1 or e2 ofinsulating material 6 that varies along the first surface contact area 7as the level of fluid in the container changes. FIG. 3 shows a sectionalview of part of the first body 1 where the thickness of the insulationis e1, and FIG. 4 shows a sectional view of part of the first body Iwhere the thickness of the insulation is e2. As a result, forcedvariations in the voltage 21 detected by the means 20 for detecting thevariability of the voltage are observed as the contact area varies froma changing fluid level 4 increases by ΔH.

To further enable the specification, it is understood by one of ordinaryskill in the art that if the first body 1 as described in the prior arthas a regular surface geometry and a constant thickness of insulationalong its length, the variability in capacitance measured by the meansfor measuring the variability of the capacitance would change along afirst slope. A change to the surface contact area in a section of thefirst body 1 in contact with the water results in a change in the slopeof the variability of the capacitance since the contact surface area Ais changed over a section of the first body 1. If the fluid level risesalong a first section 9 of the first body 1, then a first level ofvariability and a first slope is measured. Once the fluid level risesalong a second section with a different contact surface 8, the level ofvariability changes and a second slope is measured. The system 22recognizes the changes in slopes and determines junction points wherethe first body changes contact surfaces 8, 9. These junction pointscorrespond with precise heights used to recalibrate the capacitivesensor 100 at these heights in order to reduce any offset resulting froma long analogous measure and slow change in the fluid characteristics.

In one embodiment, the change in the first body surface 7 evolves alongthe length of the body according to a step function. A step function isdefined as a vertical line along the length of first body 1 wheresections of smaller resulting diameters 8 alternate with sections oflarger resulting diameters 9. The step function corresponds to a seriesof alternating fixed plateaus of two different radii as shown in FIGS.3-4. It is understood by one of ordinary skill in the art that whilestep functions and plateau regions are disclosed, any variation in thesurface sufficient to influence the variability of the capacitancemeasured by the means 20 for detecting the variability is proper andcontemplated, including but not limited to grooves, fins, otherfunctions, and even different frictions and surface finishes.

The size of the steps in the step function is also to be viewed as afunction of the measured variability of the capacitance in a certainsystem with a certain type of fluid. As a nonlimiting example, if a moreconductive fluid is used, such as sea water, the thickness variationbetween two successive sections (e1-e2) may be reduced and the steepnessof change between two plateaus in the step function may also be milder.In one embodiment, the first section 9 or the successive high sectionsas shown in FIG. 2 are 4 inches long and the second sections 8 are 7/16inches or ½ inch long. It is understood by one of ordinary skill in theart that the ensuing quantity of step functions depends on the usefullength of the first body 1 in the fluid 3.

In a preferred embodiment, the insulating material 6 is made ofpolytetrafluoethylene resins manufactured by DuPont® (Teflon®) or aTeflon®-like coating, but it is understood by one of ordinary skill inthe art that the nature and chemical composition of the properinsulating material 6 used depends on the nature and characteristics ofthe fluid. As a nonlimiting example, if the sensor 100 is used in liquidnitrogen, a very cold fluid, the insulation must maintain its insulatingproperties, not become brittle, and prevent the formation of surfacephase accumulation. The insulator in one preferred embodiment isdesigned not to accumulate particles or debris upon its surface and tonot react with the fluid over long periods of exposure. In all preferredembodiments, the fluid is water or a water-based compound with properconductive characteristics. The first body may be of cylindrical shapeand made of stainless steel, but it is understood by one of ordinaryskill in the art that any geometry may be used for the first body 1.

The means for detecting the variability in voltage 20 may include theuse of a mathematical algorithm optimized to better determine a changein the slope of the measured variability in the capacitance. In apreferred embodiment, the calculation and method for determining if achange in slope comprises the use of exponential smoothing method todetermine the changes associated with a fixed fluid level, wherein thefixed level is used to calibrate the fluid level sensing apparatus. Theexponential smoothing method consists of a series of means calculationwherein time-sensitive sample data points are taken during changes inthe variability in the capacitance and a slope for any new point iscalculated and compared with the measured data point to reveal a changein slope. One of ordinary skill in this art recognizes that while asingle method for determination and evaluation of the different slopesand their associated junction points is described, all other currentlyused methods of calculation are contemplated.

In another embodiment illustrated in FIG. 5, the insulation layer 16remains constant along the first body 1. The surface 17 of the firstbody 1 varies in radius along its vertical length along a step functionalternating from sections with a smaller radius 8 to sections with alarger radius 9. FIG. 1 shows two possible embodiments wherein theresulting change in the surface in contact with the fluid 3 alternatesfrom smaller sections 8 to larger sections 9. FIGS. 6 and 7 furtherillustrate top sectional views of the first body 1 along plane 6-6 andplane 7-7. It is understood by one of ordinary skill in the art thatwhile a single type of surface geometry is shown, what is contemplatedis an effective variation in the contact surface with the fluid 3 byvarying the surface geometry 17 of the first body 1 in order to induce avariability in the measured capacitance of the fluid. What iscontemplated is any geometry with change in the surface geometryassociated that result in a measurable and quantifiable variability involtage from the variability capacitance measurement.

In another possible embodiment as illustrated in FIG. 8, a fluid levelsensing. apparatus for placement in a container includes a sensor 100with a first body 1, a first surface contact area 15 made ofelectrically conductive material, a third body 103 with a third surfacecontact area 104 made of electrically conductive material, and a secondbody 2 with a second surface contact area 101 made of electricallyconductive material placed in opposition to the first 1 and the thirdbodies 15. The container is progressively filled with a fluid 3 in orderto change the fluid level 4. As in the first and second embodiments, thefluid 3 conductively connects a first fraction of the first surfacecontact area 15 and a third fraction of the third surface contact area104 with a second fraction of the second surface contact area 101. Thesensor 100 also is equipped with two means 21, 36 for energizing thefirst body 1 and the third body 103 to the second body 2, a first means20 for detecting the variability in voltage as the level of fluid in thecontainer changes as the first fraction of the first surface contactarea 15 and the second fraction of the second surface contact area 101changes, and a second means 105 for detecting the variability of voltage36 as the level of fluid 4 in the container changes as the thirdfraction or the third surface contact area 104 and the second fractionof the second surface contact area changes 101. The surface geometry ofthe first body 1 varies along the first, second and third surfacecontact areas 15, 104, 101 as the level of fluid 4 in the containerchanges to create forced variations in the voltage for both of the firstand second means 20, 105 for detecting the variability of the voltage.

In one embodiment, two bodies 1, 103 are placed in the fluid 3 inopposition to the second body 2. This embodiment allows for the parallelmeasurement of two different variability of capacitance, a standardizedmeasurement 20 based on a body without any variable geometryirregularities, and a measurement 36 based on a body with variablegeometry irregularities designed as described in the embodiment of thisdisclosure and shown in FIGS. 9-15, respectively. The embodiment shownin FIGS. 9-12 illustrates a situation where the probe is not insulatedand is grounded while the voltage potential is placed on the second body2. In the embodiment shown in FIGS. 13-15, the first and third bodies 1,103 are insulated 26 with a fixed thickness of insulation e1 as shown onFIGS. 14-15. The two bodies in one embodiment are shaped in asemicircular or semicylindrical vertical rod configuration placedback-to-back and made of stainless steel. The third body 103 such asthat described in the second embodiment is made of a variable surfacearea of a first step of 4-inch width separated by 7/16- or ½-inchsections forming a regular step function. While two adjacent bodies areshown, it is understood by one of ordinary skill in the art that anytwo-body geometry is contemplated as long as the external contact areasare varied appropriately in order to change the overall measure of thecapacitance of the sensor 100.

A layer of insulation 25 is placed between both the first body 1 and thethird body 103. In one embodiment, the insulation is phenolicinsulation, but it is understood by one of ordinary skill in the artthat while a single type of insulation is disclosed, what iscontemplated is an insulation 25 of a type able to effectively insulatetwo adjacent conductive bodies in a predetermined environment. FIG. 12shows a cross-section of the third body 103 illustrating notches 30created in the surface of the semicylindrical third body 103. The choiceof notches as shown in FIG. 9 corresponds in some orientation to thestep function as previously disclosed in the first and secondembodiments. In one embodiment, the notches are of a fixed width andfixed height with a flat bottom portion 29 in order to better calibratethe means for measuring the variability of the capacitance 105. It isunderstood by one of ordinary skill in the art that the third embodimentallows for the self-calibration of the sensor 100 by comparing thevariability of capacitance from the first means 20 with the variabilityof capacitance from the second means 105. It is also understood that inan alternate embodiment, the first body 1, if placed in opposition tothe third body 103, may lead to self-calibration without the second body2 by placing the means for applying a voltage difference between boththe first body 1 and the third body 103 and appropriately correcting thesurface area calculations.

In certain embodiments, the means for detecting the variability involtage between the first second body 2 and the third body 103 mayinclude the use of an exponential smoothing method to determine thechanges associated with a fixed fluid level, wherein the fixed level isused to recalibrate the fluid level sensing apparatus as disclosed inthe first and second embodiments. In another embodiment as shown in FIG.14, an insulating block 27 is placed in a notch in order to betterregulate the variability of the capacitance.

In another embodiment illustrated in FIG. 16, a fluid level sensingapparatus for placement in a container comprises a capacitance sensor 41further comprising a first body 1 with a first surface contact area 15made of electrically conductive material, a second body 2 with a secondsurface contact area 101 made of electrically conductive material placedin opposition to the first body 1, an electromechanical sensor 43further comprising a guide 40 positioned in a fluid 3 to be measured, afloat 42 mechanically connected to the guide 40 for longitudinalmovement thereon to rise and fall with the fluid level 4, a series ofreed switches 47 shown in FIG. 17 placed at fixed intervals along theguide 40, and a means for establishing a magnetic field 45 across thereed switches 47 mechanically connected with the float 42.

It is understood by one of ordinary skill in the art that thisembodiment uses a electromechanical sensor 43 to determine the actuallevel of the fluid level 4 at certain fixed positions determined by theplacement of the reed switches 47 within the vertical guide tube 40. Areed switch 47 is a small, open conductor cable placed in a glass bubble46 where both magnetized ends of the conductor are normally in an openposition. The floater 42 is hollowed and contains air or any fluid of alighter density than the fluid 3 in order to ensure that the floater 42remains on the surface 4 of the fluid. As disclosed in FIGS. 17-18, amagnet 45 is connected to the floater 42. In one preferred embodiment,the magnet 45 is located inside the floater 42 and is in contact withthe inner section of the floater 42 at its midsection. Once the floater42 reaches a certain predetermined level, the magnet 45 magnetizes thesmall conductors, which then close the electrical circuit via two cables51, 52 and send a certain signal to a detector 49 associated with theselected reed switch 47. Unlike the measure of a variation incapacitance as disclosed in the other embodiments, this embodimentproduces a signal directly associated with a fluid level. Thisembodiment also comprises a container progressively filled with fluid 3in order to change the fluid level 4. When the fluid conductivelyconnects a first fraction of the first surface contact area 15 and asecond fraction of the second surface contact area 101, and wherein thechange in fluid level changes the float 42 position along the guide 40to move the means for establishing a magnetic field 45 and close a reedswitch 47 associated with a determined fluid level. The capacitancesensor 41 as shown in FIG. 16 also includes a means for energizing thefirst body 21 and the second body at a voltage using electricalconnectors 11, 13. The means for detecting the variability in voltage 20as the level of fluid 4 in the container changes as the first fractionof the first surface contact area 15. The second fraction of the secondsurface contact area changes 101 with the change in the fluid level 4,and a means 49 such as a detector or any other means for determiningwhich reed switch 47 is closed and creates a voltage as the level of thefluid in the container changes. The determination of the level based onthe means for determining which reed switch 47 is closed is used tocorrect the determination of the level of fluid based on the means fordetecting the variability of the voltage by fixing known step levels.FIG. 17 shows a electromechanical sensor 43 where the vertical tube 40is closed by a cap 50 to prevent the fluid 3 from entering the guide 40as the level of fluid rises.

In another embodiment, shown as FIG. 18, the first body 1 is thecircular guide 40 of the electromechanical sensor 43. The first body 1is covered with a layer of insulation 26. This embodiment is equippedwith the same level of means of measure and voltage as disclosed in thepresent embodiment with the only variation that the capacitance sensor41 is merged into the electromechanical sensor 43. It is understood byone of ordinary skill in this art that while the first body 1 may betaken as the guide 40, the geometry of the floater 42 must provide asufficient passage of water in order to offer proper capacitancemeasurement.

Certain embodiments include in one embodiment thereof a circularvertical probe 40 made of stainless steel covered in the fifthembodiment by a layer of insulating Teflon® 26. In one embodiment, thereed switches 47 are separated vertically by 4 inches and the containerof the second contact surface 2 of the container is the inside wall ofthe container 101. In yet another embodiment, the fluid is water and themeans for establishing a magnetic field is a ring magnet 45 located inthe center of the floater 42. It is also contemplated that other meansfor establishing a magnetic field be used, such as a localized current,a magnet, or a magnetic element located on the surface of the water. Inanother embodiment, the floater 42 is made of a hollowed volume made ofstainless steel. It is understood by one of ordinary skill in tie artthat while a stainless steel floater is shown, any type of floater inany noncorrosive material in contact with the fluid 3 is contemplated.

FIG. 19 discloses a first method for measuring the fluid level in acontainer with a self-calibrating sensing apparatus in accordance withone embodiment of the present disclosure. The self-calibration isobtained by conducting a first step where the capacitance sensor of thefirst embodiment is placed in the container where a lower measure pointis in contact with a low level of a fluid to be measured and the highermeasure point is in contact with a high level of the fluid to bemeasured 201, a calibration of the capacitance sensor to the desiredoutput range is then performed so the lower measure point is a firstextremity of the output range and the high measure point is a secondextremity of the output range 202. The capacitance sensor and means fordetecting the variability of the voltage using a determination method torecognize variations associated with the successive levels in the stepfunction associated with the changes in thickness of the insulation arethen calibrated in order to determine precise fluid levels associatedwith each successive level in the step function 203. The capacitancesensor first determines a first level of the fluid based on the measuredoutput voltage in an analog fashion 204, and the capacitance sensor isrecalibrated at the successive levels in the step function each time theoutput voltage based with the precise fluid levels is detected 205.

One of ordinary skill in the art recognizes that an analog measure overa range can be recalibrated by the input of a predetermined value at apredetermined time and that such recalibrations are done using twodistinct measures of voltage variability. For example, if the lowerpoint corresponds to a fluid level of 2 inches and the high levelcorresponds to 20½ inches the successive levels in the step function of4 inch and ½ inch as described in a preferred embodiment of the firstembodiment, that imposes variations in slope at 6, 6½, 10½, 11, 15½, 16,and 20½ inches, respectively. As the level of fluid rises, the analogmeasure gives a fluid level reading based on its extrapolation of thevariability of the capacitance over a possible output of 4-20 mA if astandardized probe is used. For example, if the level reaches 5.95inches, the analog measure may read 5.85 or 6.05 based on the changes inthe fluid characteristics. Using the self-calibrating function, if themeasure level is above 6.00 inches, it gives a 6-inch reading and waitsfor the recognized variation associated with the level 6 inches beforeit proceeds further along its analog reading using the determined levelto recalibrate the precise fluid level. If the analog measure is lessthan 6 inches, the recalibration waits until the recognized variationassociated with the level 6 inches is activated, recalibrates the levelat 6 inches, and proceeds along its programmed calibrated range withthis new fixed value. It is understood by one of ordinary skill in theart that the use of a secondary measure to calibrate a first measurementmay be done using a plurality of different algorithms, all of whichrelate to using the measured voltage of a second sources to rectify ameasure from a first source.

A second method for measuring the fluid level in a container with aself-calibrating sensing apparatus in accordance with one embodiment ofthe present disclosure is shown in FIG. 20. The method comprises thesteps of placing the capacitance sensor in the container where a lowermeasure point is in contact with a low level of a fluid to be measuredand the higher measure point is in contact with a high level of thefluid to be measured 210, calibrating the capacitance sensor to thedesired output range so the lower measure point is a first extremity ofthe output range and the high measure point is a second extremity of theoutput range 211, calibrating the capacitance sensor and means fordetecting the variability of the voltage using a determination method torecognize variations associated with the successive levels in the stepfunction associated with the changes in irregular geometry in order todetermine precise fluid levels for recalibration associated with eachsuccessive levels in the step function 212, determining a first level ofthe fluid based on the measured output voltage of the capacitance sensor213, and recalibrating the first level of fluid associated with themeasured output voltage based with the precise fluid levels 214.

A third method for measuring the fluid level in a container with aself-calibrating sensing apparatus in accordance with one embodiment ofthe present disclosure is shown in FIG. 21. The method comprises thesteps of placing a dual-probe capacitance sensor in the container wherea lower measure point of each probe is in contact with a low level of afluid to be measured and the higher measure point of each probe is incontact with a high level of the fluid to be measured 220, calibratingeach of the two capacitance sensors to the desired output range so thelower measure point is a First extremity of the output range and thehigh measure point is a second extremity of the output range 22 1,calibrating the means for detecting the variability of the voltage inthe third body using a determination method to recognize irregularitiesin voltage associated with the irregularities in the geometry andassociating a fixed fluid level with the irregularities in geometry 222,determining a first level of the fluid based on the measured outputvoltage of the first capacitance sensor probe of a regular geometry 223,and correcting the first level of fluid associated with the measuredoutput voltage of the first probe of the capacitance sensor to the fixedfluid level determined by second probe of the capacitance sensor basedon the fluid level associated with the selected irregularities 224.

A fourth method for measuring the fluid level in a container with aself-calibrating sensing apparatus in accordance with one embodiment ofthe present disclosure is shown in FIG. 22. The method comprises thesteps of placing the capacitance sensor and the electromechanical sensorin the container where a lower measure point of each sensor is incontact with a low level of a fluid to be measured and the highermeasure point of each sensor is in contact with a high level of thefluid to be measured 231, calibrating the capacitance sensor to thedesired output range so the lower measure point is a first extremity ofthe output range and the high measure point is a second extremity of theoutput range 232, calibrating the electromechanical sensor to thedesired output range so a reed switch corresponds to a fixed outputvoltage located within the output voltage range 233, determining a firstlevel of the fluid based on the measured output voltage of thecapacitance sensor 234, and correcting the first level of fluidassociated with the measured output voltage of the capacitance sensor tothe fluid level determined by the electromechanical sensor based on thefluid level associated with the reed switch, once the fluid level of thereed switch is reached 235. In the fifth embodiment, the first body 1 ofthe capacitance sensor is the cylindrical sensor probe covered withinsulation.

A fifth method is a determination method for recognition andquantification of irregularities of a self-calibrating capacitancesensing apparatus in accordance with one embodiment of the presentdisclosure is shown in FIG. 23. The determination method comprises thesteps of determining a variability in capacitance by measuring andcomparing the capacitance over a fixed interval of time 240, associatingthe variability of capacitance with a data point 241, storing the datapoints and the quantity of data points in two arithmetic sums 242,determining a new data point to be quantified as a possible irregularity243, adding the data point to the arithmetic sums 244, reviewing theevolution of a derivative function of the arithmetic sums to determineif a change in slope is observed over a fixed number of sum intervals245, and comparing the change in the derivative function with apredetermined value to determine if a slope change is observed and if afixed fluid level is calculated 246.

It is understood by one of ordinary skill in the art that the evolutionof the derivative function of the arithmetic sums based on a method suchas the arithmetic exponential smoothing method relates to thedetermination without undue experimentation of a proper time interval ofacquisition, a proper time interval for each successive data points, aproper variability of each successive data point at the fixed timeinterval of acquisition, a determination of an equivalent sum associatedwith the arithmetic sum, an acceptable number of data points in a newpredetermined range in order to determine if a change in slope isdetermined by determining a certain number of data points to add to thesum, and a value of the new determined slope associated with the changein variability.

Persons of ordinary skill in the art appreciate that although theteachings of the disclosure have been illustrated in connection withcertain embodiments and methods, there is no intent to limit theinvention to such embodiments and methods. On the contrary, theintention of this disclosure is to cover all modifications andembodiments failing fairly within the scope the teachings of thedisclosure.

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 26. A fluid level sensing apparatus for placement in acontainer comprising: a capacitance sensor further comprising anelectrically conductive first body having a first surface contact area,an electrically conductive second body having a second surface contactarea disposed in opposition to the first body; an electromechanicalsensor further comprising a guide positioned in a fluid to be measureddisposed in the container, a float movably connected to the guide torise and fall with a fluid level, a series of reed switches disposed atpre-selected intervals along the guide, and a means for establishing amagnetic field across the reed switches, a container progressivelyfilled with the fluid in order to change the fluid level, wherein thefluid electrically couples a first fraction of the first surface contactarea and a second fraction of the second surface contact area, andwherein the change in the fluid level changes the float position alongthe guide in order to move the means for establishing a magnetic fieldand close a reed switch associated with a pre-determined fluid level, ameans for energizing the first body and the second body at a voltage; ameans for detecting the variability in voltage as the fluid level in thecontainer changes as the first fraction of the first surface contactarea and the second fraction of the second surface contact area changes;and a means for determining which reed switch is closed as the fluidlevel in the container changes, wherein the determination of the fluidlevel based on the means for determining which reed switch is closed isused to correct the determination of the fluid level based on the meansfor detecting the variability of the voltage by fixing known levelsteps.
 27. The fluid level sensing apparatus of claim 26, wherein thefirst body is a circular vertical probe made of stainless steel.
 28. Thefluid level sensing apparatus of claim 26, wherein the circular verticalprobe is covered by a polytetrafluoethylene insulation.
 29. The fluidlevel sensing apparatus of claim 26, wherein the fixed intervals alongthe guide are separated by 4 inches.
 30. The fluid level sensingapparatus of claim 26, wherein the guide of the electromechanical sensorserves as the first body of the capacitance sensor.
 31. The fluid levelsensing apparatus of claim 26, wherein the second body is the containerand the second surface contact area is the inside wall of the container.32. The fluid level sensing apparatus of claim 26, wherein the fluid iswater.
 33. The fluid level sensing apparatus of claim 26, wherein themeans of establishing a magnetic field is a ring magnet.
 34. The fluidlevel sensing apparatus of claim 33, wherein the reed switches arelocated inside a polytetrafluoethylene-encapsulated guide.
 35. The fluidlevel sensing apparatus of claim 26, wherein the float is a hollowedvolume made of stainless steel.
 36. The fluid level sensing apparatus ofclaim 33, wherein the ring magnet is located in the inner middle sectionof the float next to the guide.
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 58. A method for measuring a fluid level in a container usinga capacitance sensor and an electromechanical sensor, the capacitancesensor comprising a first conductive body and a second conductive bodyenergized by a voltage disposed in position, and a fluid electricallycoupling the first body and second body, a means for detecting thevariability in voltage as the fluid level in the container changes andproducing a output range, and the electromechanical sensor extending inthe container comprising a guide, a float movably connected to the guideincluding a means for establishing a magnetic field on a reed switchdisposed on the guide at a fixed fluid level and producing a fixedvoltage output associated with the reed switch within a output voltagerange, the method comprising the steps of: disposing the capacitancesensor and the electromechanical sensor in the container where a lowermeasure point of each sensor is in contact with a low fluid level to bemeasured and the higher measure point of each sensor is in contact witha high fluid level to be measured; calibrating the capacitance sensor tothe desired output range so the lower measure point is a first extremityof the output range and the high measure point is a second extremity ofthe output range; calibrating the electromechanical sensor to thedesired output range so the reed switch corresponds to a fixed outputvoltage within the output voltage range; determining a first fluid levelbased on the measured output voltage of the capacitance sensor;correcting the first fluid level associated with the measured outputvoltage of the capacitance sensor to the fluid level associated with thereed switch, once the fluid level of the reed switch is reached.
 59. Themethod of claim 58, wherein the first body of the capacitance sensor isa cylindrical sensor probe.
 60. The method of claim 58, wherein thesecond body of the capacitance sensor is the fluid container.
 61. Themethod of claim 58, wherein the guide of the electromechanical sensor iscovered with insulation, and wherein the first body of the capacitancesensor is the guide.
 62. The method of claim 58, wherein the capacitancesensor output range is 4-20 mA.
 63. The method of claim 58, wherein aplurality of reed switches is located inside the guide.
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